1) Field of the Invention
The invention is in the field of Semiconductor Devices.
2) Description of Related Art
For the past several years, the performance of semiconductor devices, such as Metal Oxide Semiconductor Field-Effect Transistors (MOS-FETs), has been greatly enhanced by the incorporation of shallow junctions into the active portions of a semiconductor substrate, e.g. the use of shallow tip extensions. The presence of such shallow junctions may greatly enhance the rate at which charge migrates in a channel when a semiconductor is in an ON state.
In the drive for ever-shallower junction depths, laser annealing of a dopant-implanted region of a semiconductor substrate may be utilized. Under appropriate annealing conditions, a laser anneal process may activate dopants, i.e. cause them to be substitutionally incorporated into the lattice of a substrate material, with negligible diffusion of the dopants into other regions of the substrate. This effect may be desirable because the depth of a junction may be kept confined to the implant depth of the dopant impurities, providing an ultra-shallow junction. However, the lateral diffusion of the dopants may also be restricted by the above annealing process. This may be undesirable in the case where overlap of a gate electrode over tip extensions is insufficient for optimal performance of, e.g. a MOS-FET. Thus, a method to fabricate ultra-shallow junctions is described herein.